Bony Structures of the Abdomen
The bony structures of the abdomen consist primarily of the lower thoracic vertebrae (T7-T12), lumbar vertebrae (L1-L5), portions of the lower ribs and costal cartilages, and parts of the pelvic bones.
Vertebral Components
Thoracic Vertebrae
- Lower thoracic vertebrae (T7-T12) form the posterior wall of the upper abdomen 1
- These vertebrae have distinctive features:
- Heart-shaped vertebral bodies
- Long, downward-sloping spinous processes
- Facets for articulation with ribs
Lumbar Vertebrae
- Five lumbar vertebrae (L1-L5) form the posterior wall of the middle and lower abdomen 1
- Characterized by:
- Larger, kidney-shaped vertebral bodies
- Short, blunt horizontal spinous processes
- No costal facets
- Designed to bear significant weight
Anterior and Lateral Boundaries
Costal Structures
- Lower ribs (7-12) and their costal cartilages form the upper lateral and anterolateral abdominal walls 2
- Costal margin: formed by the cartilages of ribs 7-10 joining each other before connecting to the sternum 2
- Costal arch: formed by the convergence of the costal cartilages toward the xiphoid process 3
Xiphoid Process
- Inferior-most portion of the sternum that extends into the upper abdomen 3
- Highly variable in shape - can be:
- Broad or thin
- Straight, curved, or deflected
- Monofid, bifid, or trifid
- May contain foramina
- Serves as an important anatomical landmark at the superior boundary of the abdomen 3
Pelvic Components
Iliac Bones
- The iliac wings (parts of the pelvic bones) form the lower lateral boundaries of the abdomen 4
- The iliac crests represent the superior borders of the iliac bones and serve as important landmarks for the lower abdominal boundary
Pubic Bones
- Form the anterior inferior boundary of the abdomen where it transitions to the pelvis 4
- The pubic symphysis is the midline joint between the two pubic bones
Sacrum
- Forms the posterior wall of the pelvis and lower posterior abdominal boundary 1
- Consists of five fused sacral vertebrae
- Triangular in shape, with the base articulating with L5 and the apex articulating with the coccyx
Clinical Significance
Radiographic Considerations
- Bony landmarks are essential for radiographic interpretation of abdominal imaging 5
- The vertebral bodies serve as reference points for describing locations of abdominal organs and pathology 1
- Calcification patterns of costal cartilages follow gender-related patterns and typically aren't radiographically evident until after age 30 2
Surgical Relevance
- The bony structures provide protection for abdominal organs and serve as attachment points for abdominal muscles 1
- Understanding these structures is crucial for surgical approaches to the abdomen and for proper placement of surgical incisions 1
- The costal margin must be considered when planning upper abdominal surgical access 1
Trauma Considerations
- Fractures of these structures can indicate significant trauma and may be associated with injury to underlying organs 1
- CT is the gold standard for identifying fractures of the thoracolumbar spine with a reported sensitivity of 94% to 100% 1
- Vertebral body erosion can occur with chronic contained ruptures of thoracoabdominal aortic aneurysms 1
Understanding the bony framework of the abdomen is essential for clinical assessment, radiological interpretation, and surgical planning in this anatomically complex region.